The subject matter of the invention relates to a device and to a method for manually changing a feed dog for a sewing machine.
Sewing machines each comprise one stitch-forming device for producing seams or embroidery patterns in a planar textile item, hereunder also referred to as the sewn product. The sewing machine has a machine head and an arm bed. The machine head is disposed at the end of an upper arm. A support element adjoins the other end of the upper arm. A so-called arm bed is disposed below the upper arm, so as to run substantially parallel with the upper arm. The arm bed at one end is connected to the support element. The arm bed serves as a support for the sewn product. The machine head contains a needle which is moved up and down, periodically coming into contact with the sewn product. A thread is guided in the needle. The needle pierces the sewn product. Herein, the thread is connected to a bobbin thread which is located below the sewn product, due to which a seam or a pattern is generated. The needle is releasably connected to a needle holder that is disposed at the lower end of a needle bar. The needle bar is moved up and down by a needle-bar drive. The machine head furthermore contains a presser-foot bar that has a lower end, running in a conical or a truncated-conical manner, for coupling and fastening various presser feet. Depending on the type of the sewing job to be carried out, various presser feet are employed. At the commencement of the job, the presser-foot bar together with the presser foot is lowered such that the sole of the presser foot bears on the sewn product. In this position, the sewn product is located between the feed dog and the sole of the presser foot such that the location at which a needle stitch is to take place is precisely defined. The sewn product, prior to the next stitch being performed, may be displaced to the correct position by the feed dog such that a continuous seam or a continuous pattern may be generated in this way. The feed dog thus serves for ensuring that the sewn product is indexed. Of course, the sewn product may also be manually displaced in the plane that contains the sewn product. This operating mode is employed for darning or quilting, for example. Therefore, a sewing machine may be operated according to various operating modes. Therefore, various sewing-machine types that differ in terms of the width of the feed dog used, for example, are offered nowadays. However, the width of the feed dog is established upon purchase of the sewing machine by the purchaser.
However, in order to change over between various operating modes of the sewing machine, it may be meaningful to the user to operate using a feed dog of variable width. Therefore, there is demand for a device by which the user is able to use various feed dogs. A device of this type serves for modifying the width of the feed dog or the shape of the feed dog, so as to extend the employment spectrum of a sewing machine. This sewing machine is particularly destined for the end consumer, that is to say, for use in private households.
Devices for readjusting the feed height are known from CN 10 48 78 522 A, for example, which shows a feed dog that extends in the vertical direction and that is lifted or lowered, respectively, by an eccentric feature that is attached to a shaft that is located in the arm bed, in a manner corresponding to the revolutions of the shaft. A retaining clamp for readjusting the height of a feed dog is known from CN 20 41 74 392 U. Devices for the readjustment of feed indexing are known, for example, from CN 10 43 42 853, from DE 10 2007 026 651 A1, the latter relating to an upper feed dog and to two dissimilar lower-feed readjustment drives for a first and a second lower feed dog. A feed-dog drive having a readjustable indexing direction is known from DE 3 629 514 A1. However, the prior art does not disclose any device or any method, respectively, for changing the entire feed dog, or for setting/modifying the width or the shape of the feed dog, respectively. From U.S. Pat. No. 1,992,781 it is also known for the inclination angle of the feed dog in relation to the sewn-product support to be set, wherein the width of the feed dog remains unchanged, however.
Nowadays, the user has to make a decision in favor of a sewing machine having a respective feed dog already at the point of purchase, that is to say that the width and the shape of the feed dog are permanently established as the purchase decision is made. This decision is typically made by the user by virtue of the comparatively more frequent application, or by virtue of the fundamental requirements that have to be met. Herein, the user, depending on whether the sewing machine is required more for the classic type of sewing application, or for creative sewing, decides in favor of a machine having a comparatively wide or a comparatively narrow feed dog, respectively. Accordingly, the fundamental setting is determined already by the purchase decision, limiting the user in terms of the diversity of applications. Therefore, the sewing machine in the case of many applications is outside the optimal setting in terms of the material feed.
As opposed to the case of industrial sewing machines which typically have a very narrow scope of application, or which typically enable a very small diversity of applications, respectively, and therefore are especially purchased and manufactured for few types of applications, the domestic sewing machine, independently of the purchase decision taken (for example, a width of the feed dog of 5.5 mm or 9.0 mm, respectively), must always achieve at least satisfactory results in all types of applications. For this reason, the mechanical setup, that is to say the unmodifiable basic setting of the sewing machine, so to speak, has always to be seen as a certain compromise, meaning that the material feed is optimized to the maximum for a crude field of application, for example for creative sewing or for classic sewing applications.
There is, therefore, demand for a device for pre-setting the sewing machine to a special application, for example when a special material or a special sewing technique is being used, which device does not have the disadvantages of the prior art.